#include <stdio.h>

int Number(int a,int b,int c)
{
	int val;
	switch(c)
	{
		case 1:
			val = a + b;
			break;
		case 2:
			val = a - b;
			break;
		case 3:
			val = a * b;
			break;
		case 4:
			val = a / b;
			break;
		default:
			break;
		
	}
	return val;
}

int get_Number(int a,int b,int c,int(*p)(int,int,int))
{
	int val;
	val = p(a,b,c);
	return val;
}

int main(int argc,char *argv[])
{
	int A[3];
	scanf("%d %d %d",&A[0],&A[1],&A[2]);
	if(A[1] == 0 && A[2] == 4)
	{
		return -1;
	}
	
	int ret = get_Number(A[0],A[1],A[2],Number);
	printf("ret = %d\n",ret);
	
	
	return 0;
}